Unrollable tip for a catheter

ABSTRACT

An integrated catheter assembly for enabling diverse endoscopic in situ therapies. The assembly includes a catheter with an irrigation fluid lumen, a distal electrode tip portion that acts as a hemostat, and a cutting wire for making incisions in or ablating tissue. A cutting wire hub provides a sealing entrance for a cutting wire. An operator enables the physician to displace the cutting wire between extended and retracted positions. The cutting wire and electrode are electrically isolated. In addition, the catheter assembly may include a planar tip which, when extended outside the distal end of the assembly, assumes a substantially flat unbiased configuration for use. The apparatus of the present invention allows the physician to make incisions in or ablate tissue using electrosurgery, irrigate tissue, and cauterize or coagulate tissue without having to remove the apparatus from the working channel of the endoscope.

REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 09/499,310filed Feb. 7, 2000 now U.S. Pat. No. 6,432,104, which is aContinuation-in-part of application Ser. No. 09/060,780 filed Apr. 15,1998 now U.S. Pat. No. 6,325,800, which is included herein in itsentirety by reference thereto.

FIELD OF THE INVENTION

This invention generally relates to electro-surgery,electro-cauterization and electro-coagulation of tissue in the body incombination with other forms of therapy using catheters. Specifically,this invention relates to an apparatus for performing electrosurgery,electrocauterization and electrocoagulation of tissue through a workingchannel of an endoscope.

BACKGROUND OF THE INVENTION

Numerous medical procedures involve making an incision in body tissueand controlling any consequent bleeding. When performing theseprocedures, it is very important to minimize both tissue trauma duringincision and the time required to stop internal bleeding. Minimallyinvasive or least invasive surgical techniques, such as laparoscopic,endoscopic, or arthroscopic techniques, are often used because bodytissue is usually traumatized less by those techniques than by moreinvasive conventional techniques. Electrosurgical methodologies, oftenused in conjunction with the minimally or least invasive techniques,allow the making of an incision and the stopping or stemming of bleedingwith less attendant tissue trauma and greater control than doconventional modalities.

A physician has several medical instruments in his or her armamentariumfor making an incision and stemming consequent bleeding. In accordancewith one modality that is particularly suited for application in thegastrointestinal tract, a physician initially positions a flexibleendoscope in the patient with its distal end proximate to an incisionsite, and inserts a device for making an incision through a workingchannel of the endoscope to the incision site. The physician can alsoinsert an irrigator through a working channel in the endoscope to clearthe area by administering water or saline solution as a precursor to anyattempts to make an incision or stop bleeding.

If the instrument being used for irrigation is like the Gold Probe™hemostat manufactured by Boston Scientific Corporation, the assignee ofthis invention, the physician can then cauterize a bleeding vessel usinga distally positioned hemostat. Such instruments are constructed to beemployed through a working channel of an endoscope to seal potentialbleeding sites as in the gastrointestinal tract. Alternatively, thephysician can retract the irrigating catheter and insert an elongatedneedle through the endoscope to inject a vaso-constrictor into thevessel to slow hemorrhaging. Then the physician can remove the elongatedneedle and reinsert the hemostat to finish the operation.

Some hemostats use mono-electropolar electrodes in which one electrodeis carried by a catheter to a site while the other electrode is anexterior ground plate placed in or on a patient. The above-mentionedGold Probe™ hemostat is an example of a device that supplies a suitablecurrent density and wave form of radio frequency energy to performelectro-coagulation or electro-cauterization. It utilizes a catheterwith a bipolar electrode assembly located on a flexible shaft formed ofa ceramic cylinder having a hemispherical end. The ceramic tip includesa pair of spaced gold spiral electrodes applied to its cylindricalsurface and domed end. RF energy applied to the electrodes produces acurrent through adjacent tissue that heats and cauterizes thehemorrhaging vessel which is contacted by the tip of the catheter.

Physicians often use different catheters to perform different functions.For example, physicians will often use one catheter to make an incisionand another to perform hemostasis and irrigation. The exchange ofcatheters to provide different functions extends the time to completetherapy, increases the risk to the patient and also increases patientdiscomfort. Consequently, physicians have to weigh the time, complexityand benefits of interchanging single or dual purpose catheters to changetreatment modalities against whatever disadvantage may result by workingwith a single catheter.

U.S. Pat. No. 5,336,222, the contents of which are incorporated herein,discloses an integrated catheter assembly for enabling diverse in situtherapies which includes a catheter with an irrigation fluid lumen, adistal tip portion that acts as a hemostat and a needle for injectiontherapy.

SUMMARY OF THE INVENTION

In accordance with this invention, an integrated catheter assembly thatenables a physician to utilize diverse in situ therapy modalities atselected tissue sites includes a catheter, an electrode tip and anelectrode cutting wire. A lumen extends from a proximal end to a distalend of the catheter structure to provide a passage from a locationexternally of the patient to the tissue being treated. The bipolarelectrode structure attaches to the distal end of the catheter structureand provides hemostatic therapy to selected tissue.

The electrode structure additionally has a central lumen aligned withthe catheter lumen for enabling the transfer of irrigation fluids totissue being treated. The cutting wire structure is electricallyisolated from the electrode tip and extends from a proximal endexternally of the patient through the lumens in the catheter and theelectrode structure for axially displacement relative to the catheterand electrode structures. The cutting wire can be extended distallybeyond and can be retracted proximally of a distal end surface of theelectrode tip.

In an exemplary embodiment of a catheter assembly according to thepresent invention, a distal end of the cutting wire includes asubstantially planar tip. The planar tip may be formed to achieve both aretracted, substantially circular configuration for insertion through anendoscope and for insertion of the endoscope through a lumen, and anextended, substantially planar configuration for use. The planar tip mayfurther include bipolar circuitry on at least one face.

BRIEF DESCRIPTION OF THE DRAWINGS

The various objects, advantages and novel features of this inventionwill be more fully apparent from a reading of the following detaileddescription in conjunction with the accompanying drawings in which likereference numerals refer to like parts, and in which:

FIG. 1 is a perspective view of an integrated catheter assemblyaccording to the present invention.

FIG. 2 is a side view, partially in section, of the integrated catheterassembly shown in FIG. 1, which assembly extends between proximal anddistal end portions and includes a catheter, a cutting wire and abipolar electrode assembly.

FIG. 3 is a side view, partially in section, showing in detail thedistal end portion of the apparatus in FIG. 2 including the bipolarelectrode assembly in which the cutting wire is retracted.

FIG. 4 is a side view, partially in section, showing in detail thedistal end portion of the apparatus in FIG. 2 in which the cutting wireis extended.

FIG. 5 depicts a preferred tip structure that can be substituted for thebipolar electrode assembly shown in FIGS. 3 and 4.

FIG. 6 is a side view of a cutting wire assembly used in the structureshown in FIGS. 2 through 4.

FIG. 7 is a side view of an alternate embodiment of a cutting wireassembly.

FIG. 8A is a perspective view of an exemplary integrated catheterassembly having a planar tip according to the present invention, theplanar tip being in a retracted position.

FIG. 8B is an expanded perspective view of the planar tip of 8A.

FIG. 9A is a perspective view of the assembly of FIG. 8A, with theplanar tip of 8A in an extended position.

FIG. 9B is an expanded perspective view of the planar tip of 9A.

FIG. 10 is a perspective view of an exemplary planar tip according tothe present invention.

FIG. 11 is a perspective view of a further exemplary planer tipaccording to the present invention.

FIG. 12 is another perspective view of the planar tip of FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the preferred embodiment of a electro-surgery andintervention apparatus according to the present invention, whichincludes a catheter assembly 10, a bipolar electrode tip 20, anelectrode cutting wire 23, an operator 24, an electrical cutting wireconnector 70, bipolar electrode tip connectors 2 and 4, and anirrigation hub 6.

FIG. 2 discloses the integrated catheter assembly 10 that enables aphysician to utilize diverse in situ therapy modalities at selectedtissue sites without withdrawing the assembly 10 from the workingchannel or lumen of an endoscope. It includes a modified bipolarhemostat and irrigation system 11, such as the above identified GoldProbe™ hemostat and that described in U.S. Pat. No. 5,403,311(incorporated herein by reference for its teachings). The system 11enables a physician to utilize a multipurpose device for making anincision in tissue using electrosurgery, as well as for performingbipolar hemostasis and irrigation in the treatment of a bleeding vessel.The system 11 particularly includes a catheter 12 with a single lumenthat extends from a distal location 13 to a proximal location 14. At theproximal location 14 a catheter hub 15 carries the catheter 12 from aLuer lock or similar catheter fitting 16 toward the distal location 13.Electrical leads 17 from an RF generator connector 18 also enter thecatheter hub 15. RF generators of the type utilized with this apparatusare well known and therefore not shown. The connector 18 may be onewhich connects using banana type plugs. The electrical leads 17 are ledinto the center of the catheter 12 in the hub 15 thereby to be carriedthrough a central lumen 19 of the catheter 12 to the distal location 13and a bipolar electrode assembly 20. As an alternative, the catheter 12may incorporate electrical leads in the catheter wall thereby toeliminate any contact between irrigating solutions in the lumen 19 andthe electrical leads 17. The bipolar electrode assembly 20 whenenergized over the electrical leads 17 provides hemostatic therapy.

In accordance with this invention, a wire hub 21 directs the catheter 12therethrough and supports the proximal end of a wire assembly 22 thatincludes an electrode cutting wire 23. The cutting wire 23 can movebetween extended and retracted positions by manipulation of an operator24. The operator 24 is shown at its extended position in FIG. 2 by thesolid lines and in its retracted position by phantom operator 24′. Whenthe cutting wire 23 extends distally beyond the distal end of thebipolar electrode assembly 20 as shown in FIGS. 2 and 4, it can contactand penetrate tissue, enabling a physician to make surgical incisionsinto tissue or ablate tissue.

Referring now to different sections of the apparatus shown in FIG. 2 inmore detail, FIGS. 3 and 4 depict a distal end location 13 of theintegrated catheter assembly 10. In each of FIGS. 3 and 4 the distal endof the catheter 12 terminates at the bipolar electrode assembly 20.Although the electrode assembly 20 is described as bipolar, it is wellunderstood in the art that an electrode assembly, such as the electrodeassembly 20 here, can also be monopolar. The monopolar form of theelectrode assembly 20 has only one of the spiral electrodes (i.e. 29A or29B).

More specifically the bipolar electrode assembly 20 includes acylindrical body portion 26 having a hemispherical distal end tip 27 anda proximally extending shank 28 at its other end. Discrete spiralelectrodes 29A and 29B are disposed on the outer surface of the bodyportion 26 and the end tip 27 and connect to the electrical leads 17. Adistal tip lumen 30 extends through the body portion end tip 27 andshank 28. The shank 28 is nested and supported by the catheter 12.

Still referring to FIGS. 3 and 4, a cutting wire guide portion 31includes an end section 32 that is located in the proximal end of thelumen 30 and coextensive with a portion of the shank 28. The guide wire31 can be, for example, located within a centerbore at the proximal endof the tip 27, or, as shown in FIGS. 3 and 4, within the lumen 30. Thecutting wire guide portion 31 extends proximally from the shank 28 andconstitutes a pervious guide tube for the cutting wire 23. Morespecifically, the cutting wire guide 31 is formed as a spring withmultiple spaced turns that define inter-turn passages 33. These passages33 allow fluid to transfer from the catheter lumen 19 and through thedistal tip lumen 30 to exit from the end tip 27. Fluid flow isrelatively unimpeded in the structure shown in FIG. 3 when the cuttingwire 23 is retracted. The extension of the cutting wire 23 to theposition shown in FIG. 4 restricts the distal tip lumen 30, but flow canstill occur.

FIG. 5 depicts a preferred embodiment for the bipolar electrode assembly20. In this particular embodiment, a tube 34 replaces the spring 31. Thetube 34 has a section 35 that fits in the lumen 30 and is coextensivewith a portion of the shank 28 and another section 36 that is proximalof the shank 28. This second section 36 includes a plurality of radiallyextending apertures 37 that act as passages for irrigation fluids fromthe catheter 12 through a central lumen 38.

Each of FIGS. 3 through 5 depict alternative embodiments of a bipolarelectrode assembly 20 that includes first and second electrodes 29A and29B for providing hemostatic therapy. In each embodiment a body portion26 has a hemispherical distal end 27 and carries the electrodes 29A and29B. A shank 28 extends proximally of the body portion 26 for insertioninto the lumen 19 at the distal end of the catheter 12. A tubularpervious cutting wire guide 31 extends proximally from the shank portion28 in the lumen 19 to be coextensive with the distal portion of thecatheter 12 for supporting the distal end of the cutting wire 23particularly in its retracted position.

Referring to FIG. 2, the operator 24 associated with the cutting wireassembly 22 includes a proximal end fitting 40 that can connect to acutting wire electrical connector 70 (shown in FIG. 1) which enables thecutting wire 23 to be electrically charged. At its opposite end, theoperator 24 includes a collar 41 and set screw 42 or other attachingapparatus for affixing the operator 24 to the cutting wire 23. Suchapparatus is known in the art. In this particular embodiment theoperator 24 and cutting wire 23 lie along an axis 43.

The cutting wire hub 21 can be molded or otherwise formed to include aproximal compartment 44 defined by side walls 45 and 46 and end walls 47and 48. An aperture 50 through the end wall 48 accommodates the operator24 while an aperture 51 at the distal end wall 47 accommodates thecutting wire 23. The end walls 47 and 48 support the proximal end of thecutting wire assembly 22 and limit the range of travel of the operator24 along the axis 43 between the position shown in FIG. 2 wherein thecollar 41 abuts the wall 47 and a retracted position in which the collar41 abuts the end wall 50.

An intermediate compartment 52 disposed distally of the proximalcompartment 44 supports the catheter 12 in a radiused orientation.Curved and straight side walls 53 and 54 of the cutting wire hub 21 andtransverse end walls 55 and 56 define the compartment. The end wall 55extends between the side wall 53 and 54; the end wall 56, between theside wall 53 and the intersection of the side wall 45 and end 47.Apertures 57 and 58 in the end walls 55 and 56 respectively capture thecatheter 12.

An elastomeric seal 60 surrounds the catheter 12 and is located in theintermediate compartment 52. The cutting wire 23 penetrates the seal 60and the wall of the catheter 12 thereby to be located in the catheterlumen 19 to extend through the distal tip 30 as shown in FIG. 3. Theseal 60 prevents leakage from the catheter 12 even during axialdisplacement of the cutting wire 23 along the axis 43. This seal 60generally will be formed of an elastomeric material and can take any ofseveral forms as known in the art.

The cutting wire hub 21 includes another proximal compartment 61adjacent the proximal compartment 44. The compartment 61 is formed by aproximal end wall 62, the side walls 45 and 53 and the end wall 57. Theend walls 57 and 62 in this compartment 61 support the catheter 12proximally of the seal 60 and, with the compartment 52 and end wall 55,provides an angular offset to the catheter 12 with respect to the axis43.

A distal compartment 64 is formed by the side walls 53 and 54, the endwall 55 and a distal end wall 65. An aperture 66 in the end wall 65holds the catheter 12. The end walls 55 and 65 thereby maintain thealignment of the catheter 12 along the axis 43 to facilitate theplacement and containment of the cutting wire 23 within the catheter 12lumen 19 distally of the cutting wire hub 21.

Still referring to FIG. 2, it is desirable to manufacture the cuttingwire hub 21 as a standard unit for a variety of applications. In someapplications, the limits imposed on the axial travel of the cutting wire23 by the end walls 47 and 48 may allow an extension of the cutting wire23 from the bipolar electrode assembly 20 that is greater than desired.It is possible to customize that extension by applying a positive stopstructure to the cutting wire assembly 22. One such structure is shownin FIGS. 3, 4 and 6 where like numbers refer to like elements. As shown,particularly in FIG. 6, the cutting wire assembly 22 includes theoperator 24 with its end fitting 40 and collar 41. The cutting wire 23extends as a constant diameter wire to its distal end 67. A collar 70having a distal, radially extending end surface 71 is located on aninsulated portion of the cutting wire 23 at some predetermined locationspaced from the distal end 67 by a distance that equals the length ofthe desired extension plus the distance between the end tip surface 27of the bipolar electrode assembly 20 as shown in FIG. 2 and a proximalend 72 of the cutting wire guide 31 as shown in FIGS. 3 and 4.

Consequently as the cutting wire 23 moves from its retracted position inFIG. 3 to its extended position in FIG. 4, the distal end surface 71 ofthe collar 70, that overlies the spring 31, abuts the end 72 andprevents any further distal extension of the cutting wire 23. If thebipolar electrode assembly 20 of FIG. 5 were used, the end surface 71would abut an end surface 73 on the tube 34.

FIG. 7 discloses an alternative stop mechanism wherein the cutting wireassembly 22 includes an operator 24 with proximal end connector 40 anddistal collar 41. In this embodiment the cutting wire assembly 22comprises a distal hollow section 74 and a proximal hollow section 75.The distal section 74 has a given diameter corresponding to the diameterof the cutting wire 23 shown in FIG. 6 and determined by the applicationrequirements. The length of the distal section 74 equals the desiredextension of the cutting wire plus the distance from the distal end tip27 to either end surface 72 of the guide 31 in FIGS. 3 and 4 or the endsurface 73 of the tube 34 in FIG. 5. The proximal section 75 extendsfrom the distal portion 74 to the operator 24 and has a larger diameter.Consequently the proximal portion 75 forms an annular radial surface 76at its distal end that also will abut either the end 72 of the guide 31in FIGS. 3 and 4 or the end 73 of the cutting wire guide tube 34 shownin FIG. 5.

The cutting wire 23 can be conductive along its entire length to theoperator 24, or it can have conductors which are attached at a pointalong the length of the wire 23 that is within the lumen of the catheter12. Additionally, all but the distal end of the cutting wire 23 can becoated or covered. Further, the wire 23 may be solid or hollow, in whichcase the lumen of the wire 23 can be used to allow passage of fluids forinjecting. The operator 24 can have a Luer type fitting which allowspassage of fluids for injecting and also have electrical leads to chargethe cutting wire 23

When a physician needs to make an internal incision in a patient, thephysician will, as in the prior art, insert an endoscope with a workingchannel. The physician can then insert the integrated catheter apparatus10 shown in FIG. 2 through the working channel, normally with thecutting wire 23 in its retracted position (as shown in FIG. 3). If thereis already internal bleeding in the area and it is necessary to irrigatethe area, the physician can apply irrigating fluid through the connector16 and the catheter lumen 19 to be ejected at the distal end tip 27through the lumen 30 as shown in FIGS. 2 and 3. If upon viewing the sitethe physician decides to utilize hemostasis, it is merely necessary toposition the bipolar electrode assembly 20 at the tissue and energizethe electrodes 29A and 29B. The cutting wire assembly 22 has no effecton this process. If, on the other hand, the physician determines thatthe making an incision is appropriate before or in lieu of hemostasis,the physician can easily extend the cutting wire 23 and apply and usethe cutting wire to make a surgical incision in the tissue. Thereafterthe physician can irrigate the site at will and elect to use hemostasisto stem or stop any bleeding. Each of these functions can be performedwithout withdrawing the integrated catheter apparatus 10 from theendoscope.

It will be helpful to describe some specific embodiments of thisinvention for the purpose of further understanding the construction anduse of this invention. Generally, the outer diameter of the catheter 12can be as small as 5 Fr. and as large as can be accommodated by theinner diameter of an endoscopic channel. In certain specificembodiments, for example, the catheter assembly 10 can comprise a 7 Fr.or 10 Fr. catheter 12 and a 21 gauge cutting wire 23. In an anotherembodiment, using a cutting wire as shown in FIG. 7, the distal catheterportion comprises a 23-25 gauge tubular structure while the proximalportion comprises a 21 to 22 gauge tubular structure. In addition, oneembodiment of the catheter assembly 10 in FIG. 2 extends about 220 cm.between the distal tip portion 13 and the hub 21 while the extension ofthe cutting wire 23 from the bipolar electrode assembly is limited to amaximum of 6 mm.

FIGS. 8A through 12 illustrate additional exemplary embodiments of acatheter assembly according to the present invention, and in particulara catheter assembly including a substantially planar tip 121. Ingeneral, the catheter assemblies illustrated in FIGS. 8A through 12 mayinclude elements and features similar to those described above, with theaddition of planar tip 121.

In an unbiased position, planar tip 121 has a substantially flat crosssection, where “substantially flat” is understood to mean cross-sectionswhich are flat and cross-sections which have a predetermined curvature(as shown in FIGS. 9A and 9B). In the same way, the term “planar tip” isused herein for convenience, and generally refers to any relatively flator laterally compressed surface, regardless of thickness and regardlessof whether the surface defines a plane or has a predetermined curvature.

Generally, planar tip 121 is formed of any suitable material, butpreferable one that is flexible so that, as shown in FIGS. 8A and 8B,planar tip 121 may be inserted into and through a catheter 12. In thisposition, planar tip 121 has a substantially circular cross section, asshown in FIG. 8B. This arrangement allows planar tip 121 to bend ifnecessary, to facilitate navigation to an operative position.

Once placed in an operative position, a cutting assembly which mayinclude a shaft or wire 23 can be extended to place planar tip 121 intoan extended position clear of catheter 12. Once planar tip 121 exits thedistal end of catheter 12, it may assume its unbiased, substantiallyflat configuration illustrated in FIGS. 9A and 9B. In thisconfiguration, planar tip 121 may be used as a cutting blade, or may beused as an electrocautery device, desiccation device, or ablation device(or any suitable combination thereof), as described herein.

Preferably planar tip 121 includes an electrode, which may be formed ona face of planar tip 121 by circuitry. In the illustrated embodiment ofFIG. 10, planar tip 121 includes a bipolar electrode formed by twocircuits 123 a and 123 b. Alternatively, planar tip 121 may include amonopole electrode as known in the art. When formed as a bipolarelectrode, circuits 123 a, 123 b may be in any suitable pattern.Preferably planar tip 121 is constructed of non-conductive materials, orincludes a face or coating of non-conductive materials, to separatecircuits 123 a, 123 b. Circuits 123 a and 123 b may be connect toelectrical conduits within catheter 12, as described above.

As also illustrated in FIG. 10, planar tip 121 preferably includes atapered base 125, which may be connected to shaft or wire 23. Taperedbase 125 assists planar tip 121 in “rolling” back to a retractedposition within catheter 12. In this retracted position, planar tip 121may have a generally circular cross section. It should also be notedthat while the planar tip 121 illustrated herein is generallyrectangular in shape (apart from tapered base 125), planar tip 121 maybe any suitable shape, for example circular, oval, or ovoid.

FIGS. 11 and 12 illustrate an additional exemplary embodiment of aplanar tip 121 according to the present invention. In this embodiment,planar tip 121 is fixed relative to the distal end of catheter 12,rather than movable with respect to catheter 12. In this embodiment,catheter 12 with planar tip 121 may be introduced as a unit, for examplethrough an endoscope.

Although this invention has been described in terms of a specificembodiment, and certain modifications, still other modifications can bemade. For example, cutting wire assembly 22 can comprise a one-piecemetal structure in the form shown in FIG. 6. In the form shown in FIG. 7the distal portion might be constructed of a metal while the proximalportion 75 also may include means for preventing rotation about the axis43 during use. Thus it will be apparent that these and othermodifications can be made to the disclosed apparatus without departingfrom the invention.

What is claimed is:
 1. A planar tip for a catheter assembly, comprising:a substantially planar surface having first and second faces; anelectrode disposed on the first face; means for unrolling the planar tipwhen it is extended; and means for rolling planar tip back up when it isretracted; wherein when the planar tip is in a retracted, biasedposition, the planar tip has a rolled configuration having asubstantially curved cross section, and when the planar tip is in anextended, unbiased position, the planar tip has an unrolledconfiguration having a substantially flat cross section; wherein themeans for unrolling the planar tip when it is extended comprises theelasticity of the planar tip.
 2. The planar tip according to claim 1,wherein when the planar tip is in an extended, unbiased position, theplanar tip has a slightly curved cross section.
 3. The planar tipaccording to claim 2, wherein the electrode is a bipolar electrodeformed by first and second circuits disposed on the first face, thefirst and second circuits being separated by a non-conductive portion ofthe planar surface.
 4. The planar tip according to claim 1, wherein whenthe planar tip is in an extended, unbiased position, the planar tip hasa flat cross section.
 5. The planar tip according to claim 4, whereinthe electrode is a bipolar electrode formed by first and second circuitsdisposed on the first face, the first and second circuits beingseparated by a non-conductive portion of the planar surface.
 6. A planartip for a catheter assembly, comprising: a substantially planar surfacehaving first and second faces; an electrode disposed on the first face;means for unrolling the planar tip when it is extended; and means forrolling planar tip back up when it is retracted; wherein when the planartip is in a retracted, biased position, the planar tip has a rolledconfiguration having a substantially curved cross section, and when theplanar tip is in an extended, unbiased position, the planar tip has anunrolled configuration having a substantially flat cross section;wherein the means for rolling the planar tip back up when it isretracted comprises a tapered base of the planar tip.
 7. The planar tipaccording to claim 6, wherein when the planar tip is in an extended,unbiased position, the planar tip has a slightly curved cross section.8. The planar tip according to claim 7, wherein the electrode is abipolar electrode formed by first and second circuits disposed on thefirst face, the first and second circuits being separated by anon-conductive portion of the planar surface.
 9. The planar tipaccording to claim 6, wherein when the planar tip is in an extended,unbiased position, the planar tip has a flat cross section.
 10. Theplanar tip according to claim 9, wherein the electrode is a bipolarelectrode formed by first and second circuits disposed on the firstface, the first and second circuits being separated by a non-conductiveportion of the planar surface.